This invention relates to a speed detecting system for a marine propulsion unit and more particularly to an improved dynamic pressure type of speed detecting system.
Various types of devices have been proposed for providing a speed indication for a watercraft. One device that is particularly popular and extremely effective is the so-called dynamic pressure sensitive type wherein the hull or propulsion unit is formed with a forwardly facing water inlet opening that receives dynamic water pressure as the watercraft moves through the body of water. The dynamic pressure is relatively directly related to watercraft speed. This pressure is transmitted to a remotely positioned indicator through a conduit, normally a flexible type one. There is, however, one disadvantage with this type of system.
That is, the conduit that extends from the water pressure sensing port to the instrument normally has high and low points with the highest point normally being the point where the conduit passes across the transom of the watercraft whereas the lowest point is somewhere within the hull of the watercraft. As a result of this arrangement, when the device is first installed and once the first speed indication is given, some water will pass into the conduit over the high point and collect in the low point or points. When the watercraft becomes stationary, this water is trapped in the lower points of the conduit and will create a standing pressure on the speed detector. Hence, when the watercraft next begins its travel, the speed indicator will not provide a speed indication until the water pressure exceeds the static water pressure remaining in the system. Alternatively, the device will begin to render inaccurate signals after water accumulates in the low portions of the conduit.
It is, therefore, a principal object of this invention to provide an improved speed detecting system for a watercraft.
It is a further object of this invention to provide a speed detecting system of the pressure sensitive type which does not have the aforenoted defects.